TPO253The Evolutionary Origin of PlantsWord下载.docx

TPO253The Evolutionary Origin of PlantsWord下载.docx

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Theterrestrialworldisgreennow,butitdidnotstartoutthatway.Whenplantsfirstmadethetransitionashoremorethan400millionyearsago,thelandwasbarrenanddesolate,inhospitabletolife.Fromaplant’sevolutionaryviewpoint,however,itwasalsoalandofopportunity,freeofcompetitorsandpredatorsandfullofcarbondioxideandsunlight（therawmaterialsforphotosynthesis,whicharepresentinfarhigherconcentrationsinairthaninwater）.Sooncenaturalselectionhadshapedtheadaptationsthathelpedplantsovercometheobstaclestoterrestrialliving,plantsprosperedanddiversified.

Whenplantspioneeredtheland,theyfacedarangeofchallengesposedbyterrestrialenvironments.Onland,thesupportivebuoyancyofwaterismissing,theplantisnolongerbathedinanutrientsolution,andairtendstodrythingsout.Theseconditionsfavoredtheevolutionofthestructuresthatsupportthebody,vesselsthattransportwaterandnutrientstoallpartsofplant,andstructuresthatconservewater.Theresultingadaptationstodrylandincludesomestructuralfeaturesthataroseearlyinplantevolution;

nowthesefeaturesarecommontovirtuallyalllandplant.Theyincluderootsorrootlikestructures,awaxycuticlethatcoversthesurfacesofleavesandstemsandlimitstheevaporationofwater,andporescalledstomatainleavesandstemsthatallowgasexchangebutclosewhenwaterisscarce,thusreducingwaterloss.Otheradaptationsoccurredlaterinthetransitiontoterrestriallifeandnowwidespreadbutnotuniversalamongplants.Theseincludeconductingvesselsthattransportwaterandmineralsupwardfromtherootsandthatmovethephotosyntheticproductsfromtheleavestotherestoftheplantbodyandthestiffeningsubstancelignin,whichsupporttheplantbody,helpingitexposemaximumsurfaceareatosunlight.

Theseadaptationsallowedanincreasingdiversityofplantformstoexploitdryland.Lifeonland,however,alsorequirednewmethodsoftransportingspermtoeggs.Unlikeaquaticandmarineforms,landplantscannotalwaysrelyonwatercurrentstocarrytheirsexcellsanddispersetheirfertilizedeggs.Sothemostsuccessfulgroupsoflandplantsarethosethatevolvedmethodsoffertilizedsexcelldispersalthatareindependentofwaterandstructuresthatprotestdevelopingembryosfromdryingout.Protectedembryosandwaterlessdispersalofsexcellswereachievedwiththeoriginofseedplantsandthekeyevolutionaryinnovationsthattheyintroduced:

pollen,seeds,andlater,flowersandfruits.

Paragraph1：

1.Theword“presumably”inthepassageisclosestin

meaningto

○originally

○supposedly

○obviously

○usually

2.Accordingtoparagraph1,allofthefollowingaretrueofancestralplantsEXCEPT

○Theyhadcellulose-basedcellwalls.

○Theywerecloselyrelatedtogreenalgae

○Theywereabletostorenutrients

○Theyhadasophisticatedmulticellularstructure.

Paragraph2：

Todaygreenalgaelivemainlyinfreshwater,suggestingthattheirearlyevolutionaryhistorymayhaveoccurredinfreshwaterhabitats.Ifso,thegreenalgaewouldhavebeensubjectedtoenvironmentalpressuresthatresultedinadaptationsthatenhancedtheirpotentialtogiverisetoland-dwellingororganisms.

3.Thephrase“subjectedto”inthepassageisclosestin

○restrictedby

○distantfrom

○exposedto

○combinedwith

Paragraph3：

Theenvironmentalconditionsoffreshwaterhabitats,unlikethoseofoceanhabitats,arehighlyvariable.Watertemperaturecanfluctuateseasonallyorevendailyandchanginglevelofrainfallcanleadtofluctuationsintheconcentrationofchemicalinthewateroreventoperiodinwhichtheaquatichabitatdriesup.Ancientfreshwatergreenalgaemusthaveevolvedfeaturesthatenablethemtowithstandextremesoftemperatureandperiodsofdryness.Theseadaptationsservedtheirdescendantwellastheyinvadedland.

4.Whatcanbeinferredfromparagraph3aboutancientgreenalgae?

○Theylivedinagenerallywetenvironmentthatwassometimesdry

○Theyadaptedbettertochangesinwatertemperaturethandidtootherchangesintheenvironment.

○Theyinhabitedareasthatwereclosetotheocean.

○Theyhadlivedprimarilyonland

Paragraph4:

Theterrestrialworldisgreennow,butitdidnotstartoutthatway.Whenplantsfirstmadethetransitionashoremorethan400millionyearsago,thelandwasbarrenanddesolate,inhospitabletolife.Fromaplant’sevolutionaryviewpoint,however,itwasalsoalandofopportunity,freeofcompetitorsandpredatorsandfullofcarbondioxideandsunlight（therawmaterialsforphotosynthesis,whicharepresentinfarhigherconcentrationsinairthaninwater）.Sooncenaturalselectionhadshapedtheadaptationsthathelpedplantsovercometheobstaclestoterrestrialliving,plantsprosperedanddiversified.

5.Theword“desolate”inthepassageisclosestinmeaningto

○dusty

○hardened

○deserted

○driedout

6.Whichofthesentencesbelowbestexpressestheessentialinformationinthehighlightedsentenceinthepassage?

Incorrectchoiceschangethemeaninginimportantwaysorleaveoutessentialinformation.

○Terrestrialplantshadtheadvantagesofnothavingrivalsandhavingeasyaccesstophotosyntheticmaterial

○Theabundanceofphotosyntheticmaterialmadelifeonlandeasierforpioneeringplants

○Onceplantshadeliminatedtheircompetitorsandtheirpredators,theirevolutionaryprocessproceededsmoothly.

○Plantevolutioneliminatedcompetitorsandmadetheprocessofphotosynthesismoreefficient.

7.Accordingtoparagraph4,whichofthefollowingistrueabouttheterrestrialworldatthetimeitwascolonizedbyplants?

○itwasexposedtohighlevelsofsolarradiation

○itcontainedalimitedsupplyofcarbondioxide

○ithaddeveloped400millionyearsearlier

○itlackedthepresenceofanyorganisms

Paragraph5:

nowthesefeaturesarecommontovirtuallyalllandplant.Theyincluderootsorrootlikestructures,awaxycuticlethatcoversthesurfacesofleavesandstemsandlimitstheevaporationofwater,andporescalledstomatainle